Use php extensions installer

https://github.com/mlocati/docker-php-extension-installer

Fixes https://github.com/dunglas/symfony-docker/issues/276

Dockerfile

@@ -22,6 +22,10 @@ ENV APP_ENV=prod
 
 WORKDIR /srv/app
 
+# php extensions installer: https://github.com/mlocati/docker-php-extension-installer
+ADD https://github.com/mlocati/docker-php-extension-installer/releases/latest/download/install-php-extensions /usr/local/bin/
+RUN chmod +x /usr/local/bin/install-php-extensions
+
 # persistent / runtime deps
 RUN apk add --no-cache \
 		acl \
@@ -32,37 +36,12 @@ RUN apk add --no-cache \
 	;
 
 RUN set -eux; \
-	apk add --no-cache --virtual .build-deps \
-		$PHPIZE_DEPS \
-		icu-data-full \
-		icu-dev \
-		libzip-dev \
-		zlib-dev \
-	; \
-	\
-	docker-php-ext-configure zip; \
-	docker-php-ext-install -j$(nproc) \
-		intl \
-		zip \
-	; \
-	pecl install \
-		apcu \
-	; \
-	pecl clear-cache; \
-	docker-php-ext-enable \
-		apcu \
+    install-php-extensions \
+    	intl \
+    	zip \
+    	apcu \
 		opcache \
-	; \
-	\
-	runDeps="$( \
-		scanelf --needed --nobanner --format '%n#p' --recursive /usr/local/lib/php/extensions \
-			| tr ',' '\n' \
-			| sort -u \
-			| awk 'system("[ -e /usr/local/lib/" $1 " ]") == 0 { next } { print "so:" $1 }' \
-	)"; \
-	apk add --no-cache --virtual .app-phpexts-rundeps $runDeps; \
-	\
-	apk del .build-deps
+    ;
 
 ###> recipes ###
 ###< recipes ###
@@ -125,10 +104,7 @@ RUN rm $PHP_INI_DIR/conf.d/app.prod.ini; \
 COPY docker/php/conf.d/app.dev.ini $PHP_INI_DIR/conf.d/
 
 RUN set -eux; \
-	apk add --no-cache --virtual .build-deps $PHPIZE_DEPS; \
-	pecl install xdebug; \
-	docker-php-ext-enable xdebug; \
-	apk del .build-deps
+	install-php-extensions xdebug
 
 RUN rm -f .env.local.php